1. Field of the Invention
The present invention relates to an image special effect device for transforming video data into an arbitrary shape by texture mapping, and to a graphic processor and the like that are used in the image special effect device.
2. Description of the Related Art
An image special effect device (effector) has been known as one of devices that constitute a non-linear editing system for broadcast and commercial use. The image special effect device for broadcast and commercial use is a device that performs transformation processing such as expansion, reduction and rotation of video data (moving image data) by a hardware circuit.
As for the image special effect device for broadcast and commercial use of related art, transformable patterns are limited to several kinds in advance by a manufacturer in order to avoid hardware size being enlarged and cost increase, and therefore the transformation can be performed only using the limited patterns.
On the other hand, in the field of computer graphics, an image transformation method called texture mapping is carried out by using a graphic processor that is a processor exclusively used for image processing at comparatively low cost. The texture mapping is a method in which an image (texture) is pasted to a model that is prepared by combining polygons in virtual three dimensional space.
As is known, a vertex shader for geometric processing and a pixel shader for rendering processing are installed in the graphic processor. Lately, a graphic processor in which these shaders are programmable has become the mainstream.
In the texture mapping, however, aliasing that is a phenomenon in which the edge of texture pasted is seen as jag along pixels of a display screen is caused depending on a size of the model on the display screen (this size is reduced correspondingly to a distance from a view point to a model). In a graphic processor, MIPMAP (Multum In Parvo Mapping) method is employed to control this aliasing. In the MIPMAP method, textures obtained by reducing the same image using a plurality of discrete reduction rates (1, ½, ¼, ⅛ . . . ) are stored in a memory in advance and the texture having a reduction rate close to a reduction rate of a model on the display screen is selected (refer to Japanese Published Patent Application No. 2002-83316 (paragraph No. 0004), for example).